Strong Elastic Bicomponent Fiber Having Unique Handfeel

ABSTRACT

An elastomeric bicomponent fiber, including at least one sheath and a core, with non-blocking properties and a garment-like feel is provided. The core includes two or more polypropylene based elastomers and a secondary amide, and the sheath includes a non-elastomeric polyethylene. Further, the sheath can be present as a small portion of the total elastomeric composition, and the secondary amide can be present as a small portion of the core, while forming a bicomponent fiber with non-blocking properties and a garment-like feel, while maintaining good strength characteristics.

BACKGROUND OF THE DISCLOSURE

Elastic or thermoplastic polymers, such as in the form of woven and nonwoven webs, are used in a wide variety of applications, examples of which include waistbands, side panels, leg gasketing and outercovers/backsheets for limited use or disposable products including personal care absorbent articles. As may be known in the art, such articles may include child and adult diapers, training pants, swimwear, incontinence garments, feminine hygiene products, mortuary products, wound dressings, bandages, and the like. Elastic compositions also have applications in the protective cover area, such as car, boat or other object cover components, tents (outdoor recreational covers), agricultural fabrics (row covers) and in the veterinary and health care area in conjunction with such products as surgical drapes, hospital gowns and fenestration reinforcements. Additionally, such materials have applications in other apparel for clean room and health care settings.

For instance, spunbond fabrics are formed from nonwoven webs, and have proven useful in many diverse applications. Although well suited for the above noted applications and others, existing nonwoven webs are known to have a plastic-like feel that makes the non-woven less comfortable than more “garment-like” fabrics, as they tend to lack, or have less, drapability, softness, and other tactile attributes, including cool feel. For instance, cloth, as opposed to plastic fabrics, has a more pleasing appearance, and feel, as well as having improved drape and softness. In addition, it has also proven difficult to produce nonwoven webs that have a cloth-like feel as well as adequate strength properties. Further, while elastic nonwovens, such as spunbond fabrics, have many uses, the elastic fibers tend to stick to themselves, due at least in part to the elastic polymer's low glass transition temperature (Tg) and a high degree of tackiness. This makes forming fibers and laying nonwoven webs difficult as elastic compositions tend to block between the adjacent layers, and stick to the machine during fiber formation. In the past, it was attempted to add a blocking component to an outer layer or sheath of a bicomponent fiber. However, it was found that the blocking additive failed to provide sufficient blocking and spinnability properties to the fiber.

As such, it would be a benefit to provide an elastic spunbond that exhibits non-blocking properties. Moreover, it would be a benefit to provide a bicomponent elastic fiber for forming nonwoven webs that has good elastic properties and that has a more cloth-like feel. It would be a further benefit to provide an elastic fiber for forming nonwoven webs that, such that the fiber and/or nonwoven web exhibits non-blocking properties and that can be laminated to one or more additional layers.

SUMMARY OF THE DISCLOSURE

The present disclosure is generally directed to a nonwoven web that includes an elastomeric bicomponent fiber. The elastomeric bicomponent fiber includes a core having at least two polypropylene based elastomers and a secondary amide and at least one sheath. Further, the at least one sheath forms less than 50 wt. % of the total weight of the bicomponent fiber. Further, the nonwoven web exhibits a peak burst load of about 1100 gf or greater or a normalized peak burst load of about 22 gf/gsm.

In one aspect, the nonwoven web exhibits a cup crush bending stiffness of about 100 gf or less or a normalized cup crush bending stiffness of about 2.1 gf/gsm or less. Additionally or alternatively, the nonwoven web exhibits an effusivity of about 90 Ws^(1/2)/m²K or greater.

In yet a further aspect, the at least two polypropylene based elastomers include an ethylene copolymer, α-olefin copolymer, or a combination thereof. Furthermore, in an aspect, the core further includes about 5 wt. % or less of a polypropylene homopolymer, based upon the weight of the core. In yet another aspect, the sheath includes a non-elastomeric polymer. In one aspect, the at least two polypropylene based elastomer comprise a propylene/ethylene copolymer. Further, in one aspect, the sheath includes a polyethylene polymer. Nonetheless, in yet another aspect, at least one of the sheath and the core further include pigment particles. In one aspect, the pigment particles are present in the at least one of the sheath and the core in an amount of about 0.1% to about 5% by weight based upon the weight of the sheath or the core.

Additionally or alternatively, the secondary amide is present in the core in an amount of about 0.1% to about 10% by weight based upon the weight of the core. Moreover, in one aspect, the secondary amide is present in the core in an amount of about 0.25% to about 5% by weight based upon the weight of the core. In one aspect, the secondary amide is a fatty acid amide.

The present disclosure is also generally directed to an elastomeric laminate that includes a spunbond nonwoven web according to the above, and a backing. In one aspect, the backing comprises an elastic film.

The present disclosure is also generally directed to an absorbent article formed from any aspects of the nonwoven web or the laminate discussed above.

In addition, the present disclosure is also generally directed to an elastomeric bicomponent fiber. The fiber includes a core having at least two polypropylene based elastomers and a secondary amide and at least one sheath. The at least one sheath includes less than 50 wt. % of the total weight of the bicomponent fiber; and the elastomeric bicomponent fiber exhibits a FTIR peak height ratio of an 842 cm⁻¹ peak to an 974 cm⁻¹ peak of about 0.525 or greater, as measured using a Perkin Elmer Frontier FTIR spectrometer, based upon an average of 32 scans at 4 cm⁻¹ resolution.

In one aspect, the at least two polypropylene based elastomers of the elastomeric bicomponent fiber include a first polypropylene based elastomer and a second polypropylene based elastomer, where the first polypropylene based elastomer forms about 30 wt. % or more of the core, based upon the weight of the core. In yet another aspect, the second polypropylene based elastomer of the elastomeric bicomponent fiber forms about 60 wt. % or less of the core, based upon the weight of the core. Furthermore, in one aspect, the core of the elastomeric bicomponent fiber further incudes about 15 wt % or less of a polypropylene homopolymer.

Other features and aspects of the present disclosure are described in more detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present disclosure, directed to one of ordinary skill in the art, is set forth more particularly in the remainder of the specification, which makes reference to the appended figures in which:

FIG. 1 is a schematic illustration of an apparatus that may be used to form a spunbond nonwoven web material in accordance with the present disclosure;

FIGS. 2A-2D illustrate Gray Level % Coefficient of Variation testing; and

FIGS. 3A-3C illustrate a FTIR Peak Ratio analysis according to Example 2.

Repeat use of reference characters in the present specification and drawings is intended to represent same or analogous features or elements of the disclosure.

DETAILED DESCRIPTION OF REPRESENTATIVE ASPECTS Definitions

As used herein, the terms “about,” “approximately,” or “generally,” when used to modify a value, indicates that the value can be raised or lowered by 10%, such as, such as 7.5%, 5%, such as 4%, such as 3%, such as 2%, such as 1%, and remain within the disclosed aspect. Moreover, the term “substantially free of” when used to describe the amount of substance in a material is not to be limited to entirely or completely free of and may correspond to a lack of any appreciable or detectable amount of the recited substance in the material. Thus, e.g., a material is “substantially free of” a substance when the amount of the substance in the material is less than the precision of an industry-accepted instrument or test for measuring the amount of the substance in the material. In certain example embodiments, a material may be “substantially free of” a substance when the amount of the substance in the material is less than 10%, less than 9%, less than 8%, less than 7%, less than 6%, less than 5%, less than 4%, less than 3%, less than 2%, less than 1%, less than 0.5%, or less than 0.1% by weight of the material.

As used herein, the term “elastomeric” and “elastic” and refers to a material that, upon application of a stretching force, is stretchable in at least one direction (such as the CD or MD direction), and which upon release of the stretching force, contracts/returns to approximately its original dimension. For example, a stretched material may have a stretched length that is at least 50% greater than its relaxed unstretched length, and which will recover to within at least 50% of its stretched length upon release of the stretching force. A hypothetical example would be a one (1) inch sample of a material that is stretchable to at least 1.50 inches and which, upon release of the stretching force, will recover to a length of not more than 1.25 inches. Desirably, the material contracts or recovers at least 50%, and even more desirably, at least 80% of the stretched length.

As used herein, the term “fibers” generally refer to elongated extrudates that may be formed by passing a polymer through a forming orifice, such as a die. Unless noted otherwise, the term “fibers” includes discontinuous fibers having a definite length (e.g., stable fibers) and substantially continuous filaments. Substantially filaments may, for instance, have a length much greater than their diameter, such as a length to diameter ratio (“aspect ratio”) greater than about 15,000 to 1, and in some cases, greater than about 50,000 to 1.

As used herein the term “extensible” generally refers to a material that stretches or extends in the direction of an applied force (e.g., CD or MD direction) by about 50% or more, in some aspects about 75% or more, in some aspects about 100% or more, and in some aspects, about 200% or more of its relaxed length or width.

As used herein the term “nonwoven web” generally refers to a web having a structure of individual fibers or threads which are interlaid, but not in an identifiable manner as in a knitted fabric. Examples of suitable nonwoven fabrics or webs include, but are not limited to, meltblown webs, spunbond webs, bonded carded webs, airlaid webs, coform webs, hydraulically entangled webs, and so forth.

As used herein, the term “meltblown web” generally refers to a nonwoven web that is formed by a process in which a molten thermoplastic material is extruded through a plurality of fine, usually circular, die capillaries as molten fibers into converging high velocity gas (e.g., air) streams that attenuate the fibers of molten thermoplastic material to reduce their diameter, which may be to microfiber diameter. Thereafter, the meltblown fibers are carried by the high velocity gas stream and are deposited on a collecting surface to form a web of randomly dispersed meltblown fibers. Such a process is disclosed, for example, in U.S. Pat. No. 3,849,241 to Butin, et al., which is incorporated herein in its entirety by reference thereto for all purposes. Generally speaking, meltblown fibers may be microfibers that are substantially continuous or discontinuous, generally smaller than 10 microns in diameter, and generally tacky when deposited onto a collecting surface.

As used herein, the term “spunbond web” generally refers to a web containing small diameter substantially continuous fibers. The fibers are formed by extruding a molten thermoplastic material from a plurality of fine, usually circular, capillaries of a spinnerette with the diameter of the extruded fibers then being rapidly reduced as by, for example, eductive drawing and/or other well-known spunbonding mechanisms. The production of spunbond webs is described and illustrated, for example, in U.S. Pat. No. 4,340,563 to Appel, et al., U.S. Pat. No. 3,692,618 to Dorschner, et al., U.S. Pat. No. 3,802,817 to Matsuki, et al., U.S. Pat. No. 3,338,992 to Kinney, U.S. Pat. No. 3,341,394 to Kinney, U.S. Pat. No. 3,502,763 to Hartman, U.S. Pat. No. 3,502,538 to Levy, U.S. Pat. No. 3,542,615 to Dobo, et al., and 5,382,400 to Pike, et al., which are incorporated herein in their entirety by reference thereto for all purposes. Spunbond fibers are generally not tacky when they are deposited onto a collecting surface. Spunbond fibers may sometimes have diameters less than about 40 microns, and are often between about 5 to about 20 microns.

As used herein, the term “coform” generally refers to composite materials comprising a mixture or stabilized matrix of thermoplastic fibers and a second non-thermoplastic material. As an example, coform materials may be made by a process in which at least one meltblown die head is arranged near a chute through which other materials are added to the web while it is forming. Such other materials may include, but are not limited to, fibrous organic materials such as woody or non-woody pulp such as cotton, rayon, recycled paper, pulp fluff and also superabsorbent particles, inorganic and/or organic absorbent materials, treated polymeric staple fibers and so forth. Some examples of such coform materials are disclosed in U.S. Pat. No. 4,100,324 to Anderson, et al., U.S. Pat. No. 5,284,703 to Everhart, et al., and 5,350,624 to Georger, et al., each of which are incorporated herein in their entirety by reference thereto for all purposes.

As used herein, the term “thermal point bonding” generally refers to a process performed, for example, by passing a material between a patterned roll (e.g., calender roll) and another roll (e.g., anvil roll), which may or may not be patterned. One or both of the rolls are typically heated.

As used herein, the term “ultrasonic bonding” generally refers to a process performed, for example, by passing a material between a sonic horn and a patterned roll (e.g., anvil roll). For instance, ultrasonic bonding through the use of a stationary horn and a rotating patterned anvil roll is described in U.S. Pat. No. 3,939,033 to Grgach, et al., U.S. Pat. No. 3,844,869 to Rust Jr., and 4,259,399 to Hill, which are incorporated herein in their entirety by reference thereto for all purposes. Moreover, ultrasonic bonding through the use of a rotary horn with a rotating patterned anvil roll is described in U.S. Pat. No. 5,096,532 to Neuwirth, et al., U.S. Pat. No. 5,110,403 to Ehlert, and 5,817,199 to Brennecke, et al., which are incorporated herein in their entirety by reference thereto for all purposes. Of course, any other ultrasonic bonding technique may also be used in the present disclosure.

As used herein, “formation properties” or “gray-level percent coefficient-of-variation” can be measured according to the following procedure:

The formation properties of nonwovens and similar fibrous webs can be determined using an image analysis method. The method is typically performed using transmitted or incident light with a black background. The method used here employs incident light with a black background on which the nonwoven samples are placed. Diffuse, incident lighting is provided by four LED flood lamps that are placed above and around the sample while allowing ample spacing for a camera to see down in between them onto the surface of the sample. A Leica Microsystems DFC 310 camera is used and fitted, via a c-mount, with an adjustable Nikon 35-mm lens with an f-stop setting of 4. The camera and lens assembly are mounted onto a Polaroid MP4 camera stand, or equivalent, at such a distance above the sample that provides an image field-of-view size of approximately six inches across. The camera is set in monochrome mode and a flat field correction is performed on a white background prior to analysis.

Analysis is performed by placing a nonwoven specimen onto the camera stand or automatic stage, if available, and centering it under the optical axis of the Leica DFC 310 camera and Nikon lens. The specimen must lay flat and care is taken to ensure that wrinkles or similar deformities are removed or avoided. An image analysis software package is used to monitor the illumination level, acquire an image, and then perform the measurements for determining formation. For the analysis described, a Leica Microsystems LAS software package is used to monitor the gray-level illumination for each sample between about 185-190 via an 8-bit gray-scale system. The LED flood lamps' illumination level can be controlled via a common voltage controller equipped with a knob or slider for adjustments. Alternative software packages can also be used by one skilled in the art. Once the illumination level is adjusted and set, an image is acquired and saved onto the analysis computer. The software is then used to measure the mean gray-level and gray-level standard deviation of the acquired image. Data is then electronically transmitted to and saved onto the analysis computer in an EXCEL spreadsheet. One of the basic and primary measures of formation is gray-level percent coefficient-of-variation, or

GL % COV for short. The GL % COV is calculated as follows:

GL % COV=gray-level standard deviation/mean gray-level×100%.

A minimum of five replicate analyses are performed per specimen. This is done by performing the measurements as described above on five separate regions for each specimen. After formation results are acquired, specimens can be compared to one another by performing a basic statistical analysis, such as a Student's T analysis at the 90% confidence level.

As will be discussed in greater detail herein, “A Fourier-transform infrared spectroscopy (FTIR) Peak Ratio” can be determined using common FTIR Peak Assignments as known in the art and illustrated by Table 1:

Main Raman Infrared active frequency frequency group (cm⁻¹) (cm⁻¹) vibrations — 2956vvs

2952m 2953vvs

2920m 2921vvs

2906m 2907sh

2683s 2877vs

2871w 2969vs

2840m 2840vs

1488vs 1460s

1435w 1434m

1371sh 1370s

1360s 1387m

1330vs 1326vw

1306vw 1306w

1296vw 1296vw

1257w 1255w

1219s 1220vw

1167sh 1164m

1152vs 1154w

1102w 1101vw

1040s 1045vw

999m 998m

973s 973m

941m 940vw

900m 900w

841vs 841m

809vs 809w

530m 528w

458m 456vw

398s 396vvw

321m 320vvw

252m 248vvw

Abbreviations: b = backbone, m = medium, s = strong, sh = shoulder, v = very, w = week, δ = bending, ν = stretching, ρ = rocking, τ = twisting, ω = wagging.

indicates data missing or illegible when filed

Polypropylene: AN A-Z Reference, 1999, J. Krager-Kocsis pp 320-328.

Particularly, fibers were removed from a formed nonwoven (or obtained prior to formation of the nonwoven), and were rolled flat on an aluminum coated glass slide. The FTIR spectra was then acquired using a Spotlight 400N FT-IR Imaging System in single point mode and an aperture size of 40×60 um. A microscope was connected to a Perkin Elmer Frontier FTIR spectrometer, and spectra were acquired by averaging 32 scans per sample at 4 cm⁻¹ resolution. After obtaining the spectra two or more peaks were selected for analysis, such as, to determine a height of the two or more peaks as known in the art, and a respective ratio of the two or more peak was calculated based upon the determined heights.

DETAILED DESCRIPTION

Reference now will be made in detail to various aspects of the disclosure, one or more examples of which are set forth below. Each example is provided by way of explanation, not limitation, of the disclosure. In fact, it will be apparent to those skilled in the art that various modifications and variations may be made in the present disclosure without departing from the scope or spirit of the disclosure. For instance, features illustrated or described as part of one aspect, may be used on another aspect to yield a still further aspect. Thus, it is intended that the present disclosure cover such modifications and variations.

Generally speaking, the present disclosure is directed to a bicomponent fiber that has improved spinnability, blocking, and garment-like feel, without sacrificing strength. The bicomponent fiber contains a non-elastic polyethylene or polypropylene sheath and a polypropylene based elastomeric core containing two or more polypropylene based elastomers and a secondary amide non-blocking additive. Particularly, the present disclosure has surprisingly found that when a bicomponent fiber is formed according to the present disclosure including where at least two polypropylene based elastomers and a secondary amide are included in the core, the bicomponent fiber may exhibit blocking properties, spinning properties and improved a garment-like feel, while also providing a high strength fiber. Further, these features are exhibited even when the sheath is generally free of a secondary amide blocking additive.

For instance, the bicomponent fiber according to the present disclosure may have improved softness as measured using the Cup Crush method that is discussed in greater detail in the examples below. Particularly, the lower the peak load value obtained from the cup crush test, the softer the material. Thus, in one aspect, the bicomponent fiber or a nonwoven formed therefrom according to the present disclosure may exhibit a cup crush bending stiffness of about 100 grams-force (gf) or less based upon a nonwoven web having a basis weight of about 48 gsm, such as about 50 gf or less, such as about 25 gf or less, such as about 20 gf or less, such as about 17.5 gf or less, such as about 15 gf or less, such as about 14 gf or less. Cup crush peak load can also be reported as a value normalized by the basis weight of the sample. Thus, in one aspect, the bicomponent fiber and/or nonwoven web formed therefrom can exhibit a normalized cup crush peak load of about 2.1 gf/gsm or less, such as about 2 gf/gsm or less, such as about 1.9 gf/gsm or less, such as about 1.8 gf/gsm or less, such as about 1.7 gf/gsm or less, such as about 1.6 gf/gsm or less, such as about 1.5 gf/gsm or less, such as about 1.4 gf/gsm or less, such as about 1.3 gf/gsm or less, such as about 1.2 gf/gsm or less, such as about 1.1 gf/gsm or less, such as about 1 gf/gsm or less, such as about 0.9 gf/gsm or less, such as about 0.8 gf/gsm or less, such as about 0.7 gf/gsm or less, such as about 0.6 gf/gsm or less, such as about 0.5 gf/gsm or less, such as about 0.4 gf/gsm or less, such as about 0.3 gf/gsm or less, such as about 0.25 gf/gsm or less.

Furthermore, the bicomponent fiber or a nonwoven formed therefrom according to the present disclosure may also exhibit excellent poke through, which shows that the fiber has excellent material strength while remaining soft and elastic. Thus, in one aspect, the bicomponent fiber and/or nonwoven formed therefrom may exhibit a Burst Peak Load of about 1100 gf or greater based upon a nonwoven web having a basis weight of about 48 gsm, such as about 1150 gf or greater, such as about 1200 gf or greater, such as about 1250 gf or greater, such as about 1300 gf or greater, such as about 1350 gf or greater, such as about 1400 gf or greater. Burst peak load can also be reported as a value normalized by the basis weight of the sample. Thus, in one aspect, the bicomponent fiber and/or nonwoven web formed therefrom can exhibit a normalized burst peak load of about 22 gf/gsm or greater, such as about 22.5 gf/gsm or greater, such as about 23 gf/gsm or greater, such as about 24 gf/gsm or greater, such as about 25 gf/gsm or greater, such as about 26 gf/gsm or greater, such as about 27 gf/gsm or greater, such as about 28 gf/gsm or greater, such as about 29 gf/gsm or greater, such as about 30 gf/gsm or greater.

Additionally, the present disclosure has also found that the bicomponent fiber also exhibits improved spinning properties while maintaining good elastic and strength properties and a garment-like feel. For instance, as discussed above in regards to formation, the Grey Level (GL) % Coefficient of Variation (COV) is a quantitative measure of uniformity or formation of a spunbond. Heavy areas will appear darker and light areas lighter, each being assigned a grey level. The variation in grey level of a representative image taken of the spunbond is then quantitatively evaluated for variation in local basis weight, and thus, lower greyscale variation is an indication of a more uniform material. Therefore, in one aspect, a spunbond formed using a bicomponent fiber according to the present disclosure may exhibit a GL % COV of about 27.5% or less based upon a nonwoven web having a basis weight of about 17 gsm, such as about 27% or less, such as about 26.5% or less, such as about 26% or less, such as about 25.5% or less, such as about 25% or less, such as about 24.5% or less. Furthermore, as shown in FIGS. 2A-2D, FIGS. 2A and 2C which show spunbond webs formed from bicomponent fibers containing the secondary amide in the core according to the present disclosure exhibit less variation than spunbonds formed without the secondary amide in the core (e.g. FIGS. 2B and 2D).

Furthermore, the present disclosure has found that the bicomponent fiber exhibits a cloth-like feel as exhibited by an improved thermal effusivity, the measurement of which is described in the examples below. For instance, a nonwoven web formed from the bicomponent fiber can exhibit a thermal conductivity of about 90 Ws^(1/2)/m²K or more, such as about 95 Ws^(1/2)/m²K or more, such as about 100 Ws^(1/2)/m²K or more, such as about 105 Ws^(1/2)/m²K or more, such as about 110 Ws^(1/2)/m²K or more, such as about 115 Ws^(1/2)/m²K or more, such as about 120 Ws^(1/2)/m²K or more, such as about 125 ws^(1/2)/m²K or more, such as about 130 Ws^(1/2)/m²K or more, such as about 135 Ws^(1/2)/m²K or more, such as about 150 Ws^(1/2)/m²K or more, such as about 155 Ws^(1/2)/m²K or more.

In one aspect, the secondary amide may be a fatty acid amide, such as a suitable amide compound derived from the reaction between a fatty acid and ammonia or an amine-containing compound (e.g., a compound containing a primary amine group or a secondary amine group) to yield a secondary amide. The fatty acid may be any suitable fatty acid, such as a saturated or unsaturated C₈-C₂₈ fatty acid or a saturated or unsaturated C₁₂-C₂₈ fatty acid. In certain aspects, the fatty acid may be erucic acid (i.e., cis-13-docosenoic acid), oleic acid (i.e., cis-9-octadecenoic acid), stearic acid (octadecanoic acid), behenic acid (i.e., docosanoic acid), arachic acid (i.e., arachidinic acid or eicosanoic acid), palmitic acid (i.e., hexadecanoic acid), and mixtures or combinations thereof. The amine-containing compound can be any suitable amine-containing compound, such as fatty amines (e.g., stearylamine or oleylamine), ethylenediamine, 2,2′-iminodiethanol, and 1,1′-iminodipropan-2-ol.

In one aspect, the secondary amide may be a fatty acid amide having the structure of one of Formula (I)-(III):

wherein,

R₁₄, R₁₅, R₁₆, and R₁₈ are independently selected from C₇-C₂₇ alkyl groups and C₇-C₂₇ alkenyl groups, and in some aspects, C₁₁-C₂₇ alkyl groups and C₁₁-C₂₇ alkenyl groups; and

R₁₇ is selected from C₈-C₂₈ alkyl groups and C₈-C₂₈ alkenyl groups, and in some aspects, C₁₂-C₂₈ alkyl groups and C₁₂-C₂₈ alkenyl groups.

For example, the fatty acid amide may have the structure of Formula (I) where R₁₄ is —CH₂(CH₂)₁₀CH═CH(CH₂)₇CH₃ (erucamide) and R₁₅ is —CH₂(CH₂)₁₅CH₃, or where R₁₅ is —CH₂(CH₂)₆CH═CH(CH₂)₇CH₃ (oleamide) and R₁₅ is —CH₂(CH₂)₁₃CH₃. Likewise, in yet other aspects, the fatty acid amide may have the structure of Formula (II) where R₁₆ is CH₂(CH₂)₁₅CH₃ or —CH₂(CH₂)₆CH═CH(CH₂)₇CH₃. The secondary amide may also contain a mixture of two or more such fatty acid amides. Nonetheless, in one aspect, such as the examples discussed below, the secondary amide additive is erucamide, oleamide, oleyl palmitamide, ethylene bis-oleamide, stearyl erucamide, or combinations thereof. Of course, it should be understood that, in one aspect, the secondary amide may be a non-fatty acid amide.

Regardless of the secondary amide selected, in one aspect, the secondary amide is present in the core in an amount of about 0.1% to about 10% by weight based upon the weight of the core, such as about 0.25% to about 5%, such as about 0.5% to about 2.5%, such as about 0.6% to about 1.5%, such as about 0.7% to about 1%, or any ranges or values therebetween. Particularly, the present disclosure has found that surprisingly, the secondary amide in the core provides improved spinnability and non-blocking properties to the bicomponent fiber, even when used in small amounts in the core.

Thus, in one aspect, the secondary amide may be present in the fiber in an amount of about 0.05% to about 8% based upon the weight of the fiber (e.g. weight of the core+weight of any sheath(s)), such as about 0.1% to about 4%, such as about 0.25% to about 2%, such as about 0.5% to about 1%, or any ranges or values therebetween.

In one aspect, the secondary amide may generally be a low molecular weight secondary amide having a molecular weight of about 100 g/mol to about 1000 g/mol, such as about 200 g/mol to about 900 g/mol, such as about 300 g/mol, to about 800 g/mol, such as about 400 g/mol to about 700 g/mol, or any ranges or values therebetween.

Notwithstanding the secondary amide selected, the present disclosure has also found that, while the secondary amide may also improve the garment-like feel of the fiber and resulting nonwoven, the garment-like feel of the fiber may be further improved by forming a bicomponent fiber having at least one sheath formed from a non-elastomeric polyethylene or polypropylene polymer, in conjunction with a polypropylene based elastomer core containing two or more polypropylene based elastomers in conjunction with the secondary amide. Thus, in one example, the bicomponent elastomeric fiber according to the present disclosure may display elastic properties before and after being wound into a roll or spool, and may also have blocking properties that allows the fiber to be unwound from the roll or spool while maintaining a garment-like feel. Furthermore, it has been found that the excellent non-blocking properties are exhibited even when the one or more sheath(s) form less than about 50%, such as about 45% or less, such as about 40% by weight or less of the total weight of the elastomeric composition, such as about 35% or less, such as about 30% or less, such as about 25% or less, such as about 20% or less, such as about 15% or less, such as about 10% or less of the total weight of the elastomeric composition.

Regardless of the number of the number of sheaths, in one aspect, an elastomer that may be used in the core may be formed from one or more of a variety of thermoplastic elastomeric and plastomeric polymers, such as elastomeric polyesters, elastomeric polyurethanes, elastomeric polyamides, elastomeric copolymers, elastomeric polyolefins, and so forth. In one particular aspect, elastomeric semi-crystalline polyolefins are employed due to their unique combination of mechanical and elastomeric properties. Semi-crystalline polyolefins have or are capable of exhibiting a substantially regular structure. For example, semi-crystalline polyolefins may be substantially amorphous in their undeformed state, but form crystalline domains upon stretching. The degree of crystallinity of the olefin polymer may be from about 3% to about 60%, in some aspects from about 5% to about 45%, in some aspects from about 10% to about 40%, and in some aspects, from about 15% and about 35%. Likewise, the semi-crystalline polyolefin may have a latent heat of fusion (ΔH_(f)), which is another indicator of the degree of crystallinity, of from about 15 to about 210 Joules per gram (“J/g”), in some aspects from about 20 to about 100 J/g, in some aspects from about 20 to about 65 J/g, and in some aspects, from 25 to about 50 J/g. The semi-crystalline polyolefin may also have a Vicat softening temperature of from about 10° C. to about 100° C., in some aspects from about 20° C. to about 80° C., and in some aspects, from about 30° C. to about 60° C. The semi-crystalline polyolefin may have a melting temperature of from about 20° C. to about 120° C., in some aspects from about 35° C. to about 90° C., and in some aspects, from about 40° C. to about 80° C. The latent heat of fusion (ΔH_(f)) and melting temperature may be determined using differential scanning calorimetry (“DSC”) in accordance with ASTM D-3417 as is well known to those skilled in the art. The Vicat softening temperature may be determined in accordance with ASTM D-1525.

Exemplary semi-crystalline polyolefins include polyethylene, polypropylene, as well as their blends and copolymers thereof. In one particular aspect, a polyethylene is employed that is a copolymer of ethylene and an α-olefin, such as a C₃-C₂₀ α-olefin or C₃-C₁₂ α-olefin. Suitable α-olefins may be linear or branched (e.g., one or more C₁-C₃ alkyl branches, or an aryl group). Specific examples include 1-butene; 3-methyl-1-butene; 3,3-dimethyl-1-butene; 1-pentene; 1-pentene with one or more methyl, ethyl, or propyl substituents; 1-hexene with one or more methyl, ethyl, or propyl substituents; 1-heptene with one or more methyl, ethyl or propyl substituents; 1-octene with one or more methyl, ethyl or propyl substituents; 1-nonene with one or more methyl, ethyl or propyl substituents; ethyl, methyl or dimethyl-substituted 1-decene; 1-dodecene; and styrene. Particularly desired α-olefin comonomers are 1-butene, 1-hexene, and 1-octene. The ethylene content of such copolymers may be from about 60 mole % to about 99 mole %, in some aspects from about 80 mole % to about 98.5 mole %, and in some aspects, from about 87 mole % to about 97.5 mole %. The α-olefin content may likewise range from about 1 mole % to about 40 mole %, in some aspects from about 1.5 mole % to about 15 mole %, and in some aspects, from about 2.5 mole % to about 13 mole %.

The density of the polyethylene may vary depending on the type of polymer employed, but generally ranges from about 0.85 g/cm³ to about 0.96 g/cm³. Polyethylene “plastomers”, for instance, may have a density in the range of from 0.85 g/cm³ to 0.91 g/cm³. Likewise, “linear low density polyethylene” (“LLDPE”) may have a density in the range of from about 0.91 g/cm³ to about 0.94 g/cm³; “low density polyethylene” (“LDPE”) may have a density in the range of from about 0.91 g/cm³ to about 0.94 g/cm³; and “high density polyethylene” (“HDPE”) may have density in the range of from 0.94 g/cm³ to 0.96 g/cm³. Densities may be measured in accordance with ASTM 1505.

Particularly suitable polyethylene copolymers are those that are “linear” or “substantially linear.” The term “substantially linear” means that, in addition to the short chain branches attributable to comonomer incorporation, the ethylene polymer also contains long chain branches in the polymer backbone. “Long chain branching” refers to a chain length of at least 6 carbons. Each long chain branch may have the same comonomer distribution as the polymer backbone and be as long as the polymer backbone to which it is attached. Preferred substantially linear polymers are substituted with from 0.01 long chain branch per 1000 carbons to 1 long chain branch per 1000 carbons, and in some aspects, from 0.05 long chain branch per 1000 carbons to 1 long chain branch per 1000 carbons. In contrast to the term “substantially linear”, the term “linear” means that the polymer lacks measurable or demonstrable long chain branches. That is, the polymer is substituted with an average of less than 0.01 long chain branch per 1000 carbons.

The density of a linear ethylene/α-olefin copolymer is a function of both the length and amount of the α-olefin. That is, the greater the length of the α-olefin and the greater the amount of α-olefin present, the lower the density of the copolymer. Although not necessarily required, linear polyethylene “plastomers” are particularly desirable in that the content of α-olefin short chain branching content is such that the ethylene copolymer exhibits both plastic and elastomeric characteristics—i.e., a “plastomer.” Because polymerization with α-olefin comonomers decreases crystallinity and density, the resulting plastomer normally has a density lower than that of polyethylene thermoplastic polymers (e.g., LLDPE), but approaching and/or overlapping that of an elastomer. For example, the density of the polyethylene plastomer may be 0.91 g/cm³ or less, in some aspects, from about 0.85 g/cm³ to about 0.88 g/cm³, and in some aspects, from about 0.85 g/cm³ to about 0.87 g/cm³. Despite having a density similar to elastomers, plastomers generally exhibit a higher degree of crystallinity and may be formed into pellets that are non-adhesive and relatively free flowing.

The distribution of the α-olefin comonomer within a polyethylene plastomer is typically random and uniform among the differing molecular weight fractions forming the ethylene copolymer. This uniformity of comonomer distribution within the plastomer may be expressed as a comonomer distribution breadth index value (“CDBI”) of 60 or more, in some aspects 80 or more, and in some aspects, 90 or more. Further, the polyethylene plastomer may be characterized by a DSC melting point curve that exhibits the occurrence of a single melting point peak occurring in the region of 50 to 110° C. (second melt rundown).

Suitable plastomers for use in the present disclosure are ethylene-based copolymer plastomers available under the designation EXACT™ from ExxonMobil Chemical Company of Houston, Tex., ENGAGE™ and AFFINITY™ from Dow Chemical Company of Midland, Mich., and olefin block copolymers available from Dow Chemical Company of Midland, Mich. under the trade designation INFUSE™, such as INFUSE™ 9807. A polyethylene that can be used in a fiber of the present disclosure is DOW™ 61800.41. Still other suitable ethylene polymers are available from The Dow Chemical Company under the designations DOWLEX™ (LLDPE), ASPUN™ (LLDPE), and ATTANE™ (ULDPE). Other suitable ethylene polymers are described in U.S. Pat. No. 4,937,299 to Ewen et al; U.S. Pat. No. 5,218,071 to Tsutsui et al.; U.S. Pat. No. 5,272,236 to Lai, et al.; and 5,278,272 to Lai, et al., which are incorporated herein in their entirety by reference thereto for all purposes.

Nonetheless, as discussed above, it should be understood that, in one aspect, the one or more sheaths is/are formed from one or more ethylene or propylene polymers, such as one or more generally non-elastomeric ethylene or propylene polymers. Thus, in one aspect, the non-elastomeric polyolefin may include generally inelastic polymers, such as conventional polyolefins, (e.g., polyethylene), low density polyethylene (LDPE), Ziegler-Natta catalyzed linear low density polyethylene (LLDPE), etc.), ultra low density polyethylene (ULDPE), polypropylene, polybutylene, etc.; polytetrafluoroethylene; polyesters, e.g., polyethylene terephthalate (PET), etc.; polyvinyl acetate; polyvinyl chloride acetate; polyvinyl butyral; acrylic resins, e.g., polyacrylate, polymethylacrylate, polymethylmethacrylate, etc.; polyamides, e.g., nylon; polyvinyl chloride; polyvinylidene chloride; polystyrene; polyvinyl alcohol; polyurethanes; polylactic acid; copolymers and mixtures thereof; and so forth. For instance, the sheath(s) can include an LLDPE available from Dow Chemical Co. of Midland, Mich., such as DOWLEX™ 2517 or DOWLEX™ 2047, or a combination thereof, or Westlake Chemical Corp. of Houston, Tex. Furthermore, in one aspect, the non-blocking polyolefin material may be other suitable ethylene polymers, such as those available from The Dow Chemical Company under the designations ASPUN™ (LLDPE) and ATTANE™ (ULDPE). available from The Dow Chemical Company under the designations DOWLEX™ (LLDPE), ASPUN™ (LLDPE), and ATTANE™ (ULDPE).

Regardless of the polymer(s) selected for the one or more sheath(s), the core may be formed from two or more semi-crystalline polyolefins as discussed above. For instance, propylene polymers may also be suitable for use as a semi-crystalline polyolefin. Suitable plastomeric propylene polymers may include, for instance, copolymers or terpolymers of propylene include copolymers of propylene with an α-olefin (e.g., C₃-C₂₀), such as ethylene, 1-butene, 2-butene, the various pentene isomers, 1-hexene, 1-octene, 1-nonene, 1-decene, 1-unidecene, 1-dodecene, 4-methyl-1-pentene, 4-methyl-1-hexene, 5-methyl-1-hexene, vinylcyclohexene, styrene, etc. The comonomer content of the propylene polymer may be about 35 wt. % or less, in some aspects from about 1 wt. % to about 20 wt. %, and in some aspects, from about 2 wt. % to about 10 wt. %. Preferably, the density of the polypropylene (e.g., propylene/α-olefin copolymer) may be 0.91 grams per cubic centimeter (g/cm³) or less, in some aspects, from 0.85 to 0.88 g/cm³, and in some aspects, from 0.85 g/cm³ to 0.87 g/cm³. Suitable propylene-based copolymer plastomers are commercially available under the designations VISTAMAXX™ (e.g., 2330, 6202, and 6102), a propylene-ethylene copolymer-based plastomer from ExxonMobil Chemical Co. of Houston, Tex.; FINA™ (e.g., 8573) from Atofina Chemicals of Feluy, Belgium; TAFMER™ available from Mitsui Petrochemical Industries; and VERSIFY™ available from Dow Chemical Co. of Midland, Mich. Other examples of suitable propylene polymers are described in U.S. Pat. No. 6,500,563 to Datta, et al.; U.S. Pat. No. 5,539,056 to Yang, et al.; and 5,596,052 to Resconi, et al., which are incorporated herein in their entirety by reference thereto for all purposes.

However, it should be understood that, in one aspect, the core is formed from a propylene polymer and/or copolymer. Thus, in one aspect, the core is formed from a propylene-based copolymer plastomers, such as a propylene-based copolymer commercially available under the designations VISTAMAXX™ (e.g., 2330, 6202, 6102, and 7050), a propylene-ethylene copolymer-based plastomer from ExxonMobil Chemical Co. of Houston, Tex.; FINA™ (e.g., 8573) from Atofina Chemicals of Feluy, Belgium; TAFMER™ available from Mitsui Petrochemical Industries; and VERSIFY™ available from Dow Chemical Co. of Midland, Mich.

Nonetheless, in one aspect, a combination of two or more polypropylene elastomers may be selected in order to form a more ordered structure with closely aligned chains. Thus, in one aspect, a first polypropylene elastomer may be present in the core in an amount of about 30 wt. % or greater, such as about 35 wt. % or greater, such as about 37.5 wt. % or greater such as about 40 wt. % or greater, such as about 45 wt. % or greater, such as about 50 wt. % or greater, such as about 55 wt. % or greater, such as about 60 wt. % or greater, up to about 95 wt. %, or any ranges or values therebetween, based upon the weight of the core. The first polypropylene elastomer can have a density of less than 0.867 g/m³, such as about 0.865 g/m³ or less, such as about 0.862 g/m³ or less, such as down to about 0.86 g/m³. In one aspect, the first polypropylene elastomer may be considered to be a low-density polypropylene elastomer. For instance, such polypropylene elastomers may be sold under the tradename VISTAMAXX™, such as VISTAMAXX 7050, for example.

Further, the second polypropylene elastomer may be present in the core in an amount of about 65 wt. % or less, such as about 60 wt. % or less, such as about 55 wt. % or less, such as about 50 wt. % or less, such as about 45 wt. % or less, such as about 40 wt. % or less, such as about 5 wt. % or greater, or any ranges or values therebetween, based upon the weight of the core. The second polypropylene elastomer can have a density of greater than 0.867 g/m³, such as about 0.868 g/m³ or greater, such as about 0.87 g/m³ or greater, such as about 0.88 g/m³ or greater, such as about 0.89 g/m³ or greater, such as up to about 0.9 g/m³. In one aspect, the second polypropylene elastomer may be considered to be a high-density polypropylene elastomer Such polypropylene elastomers may be sold under the tradename VERSIFY™, such as VERSIFY 4301 and/or VERSIFY 4200.

Particularly, without wishing to be bound by theory, the present disclosure has found that when a blend of polypropylene polymers as described herein are used to form a core, a more ordered and packed polymer chain is observed. As will be discussed in greater detail below, when using two or more polypropylene polymers as discussed herein, the polymer chains are able to align in a more ordered structure that is not achievable when using either a low-density co-polymer or a high density co-polymer alone. Thus, in one aspect, the amount of first polypropylene elastomer and an amount of the second polypropylene elastomer in the core are selected based upon the above amounts so as to provide a peak height ratio of a 842 cm⁻¹ FTIR peak to the 974 cm⁻¹ FTIR peak (indicating greater alignment and a more ordered chain) of the core composition of about 0.52 or greater, such as about 0.55 or greater, such as about 0.58 or greater, such as about 0.6 or greater such as about 0.63 or greater, such as about 0.65 or greater, measured according to the FTIR peak height ratio discussed above.

Additionally, in one aspect, a small amount of spunbond grade polypropylene with no α-olefin co-monomer, such as a polypropylene homopolymer, also referred to as a spunbond grade polypropylene, can be included in the core in order to further improve the strength properties of the fiber. However, when present, spunbond grade polypropylene is present in an amount of about 15 wt. % or less, such as about 12.5 wt. % or less, such as about 10 wt. % or less, such as about 7.5 wt. % or less, such as about 5 wt. % or less, such as about 4 wt. % or less, such as about 3 wt. % or less, such as about 2 wt. % or less, such as about 1 wt. % or less, based upon the weight of the core formulation.

Particularly, when present, the spunbond grade polypropylene is present in an amount sufficient to impart strength properties without affecting the cloth-like feel.

Any of a variety of known techniques may generally be employed to form the semi-crystalline polyolefins. For instance, olefin polymers may be formed using a free radical or a coordination catalyst (e.g., Ziegler-Natta). Preferably, the olefin polymer is formed from a single-site coordination catalyst, such as a metallocene catalyst. Such a catalyst system produces ethylene copolymers in which the comonomer is randomly distributed within a molecular chain and uniformly distributed across the different molecular weight fractions. Metallocene-catalyzed polyolefins are described, for instance, in U.S. Pat. No. 5,571,619 to McAlpin et al.; U.S. Pat. No. 5,322,728 to Davis et al.; U.S. Pat. No. 5,472,775 to Obiieski et al.; U.S. Pat. No. 5,272,236 to Lai et al.; and 6,090,325 to Wheat, et al., which are incorporated herein in their entirety by reference thereto for all purposes. Examples of metallocene catalysts include bis(n-butylcyclopentadienyl)titanium dichloride, bis(n-butylcyclopentadienyl)zirconium dichloride, bis(cyclopentadienyl)scandium chloride, bis(indenyl)zirconium dichloride, bis(methylcyclopentadienyl)titanium dichloride, bis(methylcyclopentadienyl)zirconium dichloride, cobaltocene, cyclopentadienyltitanium trichloride, ferrocene, hafnocene dichloride, isopropyl(cyclopentadienyl,-1-flourenyl)zirconium dichloride, molybdocene dichloride, nickelocene, niobocene dichloride, ruthenocene, titanocene dichloride, zirconocene chloride hydride, zirconocene dichloride, and so forth. Polymers made using metallocene catalysts typically have a narrow molecular weight range. For instance, metallocene-catalyzed polymers may have polydispersity numbers (MW/Mn) of below 4, controlled short chain branching distribution, and controlled isotacticity.

The melt flow index (MI) of the semi-crystalline polyolefins may generally vary, but is typically in the range of about 0.1 grams per 10 minutes to about 100 grams per 10 minutes, in some aspects from about 0.5 grams per 10 minutes to about 50 grams per 10 minutes, and in some aspects, about 1 to about 35 grams per 10 minutes, such as about 1.5 to about 25 grams per 10 minutes, determined at 190° C. The melt flow index is the weight of the polymer (in grams) that may be forced through an extrusion rheometer orifice (0.0825-inch diameter) when subjected to a force of 5000 grams in 10 minutes at 190° C., and may be determined in accordance with ASTM Test Method D1238-E.

While the elastomer(s) have been thus far discussed for both the core and the sheath, it should be understood that the core and the sheath may contain the same elastomer(s) or a different elastomer or elastomer(s). For instance, in one aspect, the core may contain two or more polypropylene based copolymer elastomer, such as a polypropylene/ethylene copolymer, as discussed above (e.g., VISTAMAXX™ and/orVERSIFY™ alone or in combination with a further propylene polymer), whereas the sheath may contain a non-elastic polyethylene polymer (e.g., ASPUN™).

Nonetheless, as discussed above, the present disclosure has found that by including a non-elastomeric polyolefin material in combination with a core containing a propylene based elastomer and a secondary amide, a non-blocking bicomponent fiber can be formed that exhibits a garment-like feel, and that also exhibits improved spinnability and blocking even though the secondary amide is contained in the core.

Notwithstanding the elastomer(s) selected for the sheath and core, and/or the non-elastomeric polyolefin selected for the sheath, a single polymer as discussed above can be used to form the elastomer and/or the non-elastomeric polyolefin of the core, the sheath, or both the core and the sheath in amount up to 100 wt. % based on the total weight of the nonwoven web material, such as from about 75 wt. % to about 99 wt. %, such as from about 80 wt. % to about 98 wt. %, such as from about 85 wt. % to about 95 wt. %. However, in other aspects, the elastomer and/or the non-elastomeric polyolefin can include two or more polymers from the polymers discussed above.

Furthermore, regardless of the elastomer(s) and non-elastomeric polyolefin selected, in one aspect the core is present in an amount of about 50% to about 97.5% by weight of the total weight of the elastomeric composition, such as about 60% to about 95%, such as about 70% to about 92.5%, such as about 80% to about 90%, such as about 82.5% to about 87.5% by weight of the total weight of the elastomeric composition, or any ranges or values therebetween.

Furthermore, in one aspect, the sheath may include one or more inorganic fillers, either in addition to, or instead of, the non-elastic polyolefin. Thus, in one aspect, the sheath includes one or more of calcium carbonate (CaCO₃), various kinds of clay, silica (SO₂), alumina, barium sulfate, sodium carbonate, talc, magnesium sulfate, titanium dioxide, zeolites, aluminum sulfate, cellulose-type powders, diatomaceous earth, magnesium sulfate, magnesium carbonate, barium carbonate, kaolin, mica, carbon, calcium oxide, magnesium oxide, aluminum hydroxide, pulp powder, wood powder, cellulose derivative, polymer particles, chitin and chitin derivatives. In one aspect, the inorganic particles may include calcium carbonate, diatomaceous earth, or combinations thereof.

In one aspect, the sheath, the core, or both the sheath and the core may include pigment particles. In one aspect, the sheath, the core, or both the sheath and the core includes about 0.1% to about 5% by weight pigment particles based upon the total weight of the sheath, such as about 0.5% to about 4.5%, such as about 1% to about 4%, such as about 1.5% to about 3.5%, or any ranges or values therebetween.

Furthermore, in one aspect, the sheath, core, or both the sheath and the core may include a wetting agent to impart wettability to the bicomponent fiber. In such an aspect, the sheath, the core, or both the sheath and the core include about 10 wt. % or less of a wetting agent based upon the weight of the respective sheath and/or core, such as about 9 wt. % or less, such as about 8 wt. % or less, such as about 7 wt. % or less, such as about 5 wt. % or less, such as about 2.5 wt. % or less. In one aspect, both the core and sheath may include a wetting agent according to the above discussed amounts, however, it should be understood that the above referenced amounts may also be in regards to the total amount of wetting agent in the sheath and core. Furthermore, in one aspect, the sheath and core do not contain a wetting agent.

Notwithstanding the final polymer(s) and additive selected, the bicomponent fiber containing the secondary amide according to the present disclosure may exhibit excellent properties. For instance, in one aspect, a fiber according to the present disclosure may exhibit a hysteresis loss of about 80% or less, such as about 75% or less, such as about 72.5% or less, such as about 70% or less, such as about 67.5% or less, based upon a nonwoven web having a basis weight of about 48 gsm, for which testing methods are defined in greater detail in the examples below, or any ranges or values therebetween.

Furthermore, a fiber may exhibit a percent set of about 20% or less, such as about 17.5% or less, such as about 15% or less, such as about 12.5% or less, such as about 11% or less, at 30% elongation, based upon a nonwoven web having a basis weight of about 48 gsm, as discussed in greater detail in the examples below, or any ranges or values therebetween.

For instance, in some aspect, the fibers can have a sheath-core arrangement where the sheath can form about 50% by weight or less of the total weight of the fiber, such as about 45% or less, such as about 40% or less, such as about 35% or less, such as about 30% or less, such as about 25% or less, such as about 20% or less, such as about 15% or less, such as about 10% or less of the total weight of the fiber. Furthermore, in one aspect, the core may form from about 50% to about 97.5% by weight of the total weight of the fiber, such as about 60% to about 95%, such as about 70% to about 92.5%, such as about 80% to about 90% by weight of the total weight of the fiber, or any ranges or values therebetween.

Nonetheless, in one aspect, the present disclosure may also generally include forming a spunbond web using elastomeric bicomponent fibers according to the present disclosure.

Regardless of the specific polymers employed, a variety of techniques may generally be employed to form a spunbond web formed from elastomeric bicomponent fibers of the present disclosure. For example, in one aspect, the spunbond web may be formed by a spunbond process in which two or more polymer compositions are fed to an extruder and extruded through a conduit to a spinneret. Spinnerets for extruding fibers are well known to those of skill in the art. For example, the spinneret may include a housing containing a spin pack having a plurality of plates stacked one on top of each other and having a pattern of openings arranged to create flow paths for the polymer composition. The spinneret may also have openings arranged in one or more rows that form a downwardly extruding curtain of fibers when the polymer composition is extruded therethrough. The process may also employ a quench blower positioned adjacent the curtain of fibers extending from the spinneret. Air from the quench air blower may quench the fibers as they are formed. A fiber draw unit or aspirator may also be positioned below the spinneret to receive the quenched fibers. Fiber draw units or aspirators for use in melt spinning polymers are well-known in the art. The fiber draw unit may include an elongate vertical passage through which the fibers are drawn by aspirating air entering from the sides of the passage and flowing downwardly through the passage. A heater or blower may supply aspirating air to the fiber draw unit, which draws the fibers and ambient air through the fiber draw unit.

Generally speaking, the resulting fibers have an average size (e.g., diameter) of about 100 micrometer or less, in some aspects from about 0.1 microns to about 50 microns, such as from about 0.5 microns to about 40 microns, such as from about 1 micron to about 30 microns, such as from about 2.5 microns to about 20 microns, or any ranges or values therebetween.

Regardless of the form of the spunbond web, additives may also be incorporated into the spunbond web, or the fibers formed therefrom, such as melt stabilizers, processing stabilizers, heat stabilizers, light stabilizers, antioxidants, heat aging stabilizers, whitening agents, antiblocking agents, viscosity modifiers, etc. Viscosity modifiers may also be employed, such as polyethylene wax (e.g., EPOLENE™ C-10 from Eastman Chemical). Phosphite stabilizers (e.g., IRGAFOS available from Ciba Specialty Chemicals of Tarrytown, N.Y. and DOVERPHOS available from Dover Chemical Corp. of Dover, Ohio) are exemplary melt stabilizers. In addition, hindered amine stabilizers (e.g., CHIMASSORB available from Ciba Specialty Chemicals) are exemplary heat and light stabilizers.

Further, hindered phenols are commonly used as an antioxidant in the production of films. Some suitable hindered phenols include those available from Ciba Specialty Chemicals of under the trade name IRAGANOX™, such as IRGANOX™ 1076, 1010, or E 201. When employed, such additives (e.g., antioxidant, stabilizer, etc.) may each be present in an amount from about 0.001 wt. % to about 25 wt. %, in some aspects, from about 0.005 wt. % to about 20 wt. %, and in some aspects, from 0.01 wt. % to about 15 wt. % of the nonwoven web material.

Referring now to FIG. 1 , various aspects of the fiber forming process will be discussed.

Referring to FIG. 1 , for instance, one aspect of a process for forming fibers that can be employed in the present disclosure is shown in more detail. Although by no means required, the process shown in FIG. 1 is configured to form bicomponent substantially continuous fibers having an A/B configuration. More particular, polymer compositions A and B are initially supplied to a fiber spinning apparatus 21 to form bicomponent fibers 23. Once formed, the fibers 23 are traversed through a fiber draw unit 25 and deposited on a moving forming wire 27. Deposition of the fibers is aided by an under-wire vacuum supplied by a suction box 29 that pulls down the fibers 23 onto the forming wire 27. The forming wire 27 is porous so that vertical air flow created by the suction box 29 can cause the fibers to lie down. In one aspect of the present disclosure, the flow rate of this air flow can be kept relatively low to enhance the tendency of the fibers 23 to remain oriented in the MD direction. Alternatively, the suction box can contain sections that extend in the machine direction to disrupt the vertical air flow with at the point where the fibers are laid onto the moving web, thereby allowing the fibers to have a higher degree of orientation in the machine direction. One example of such a technique is described, for instance, in U.S. Pat. No. 6,331,268. Of course, other techniques may also be employed to help fibers remain oriented in the machine direction. For example, deflector guide plates or other mechanical elements can be employed, such as described in U.S. Pat. Nos. 5,366,793 and 7,172,398. The direction of the air stream used to attenuate the fibers as they are formed can also be used to adjust to effect machine direction orientation, such as described in U.S. Pat. No. 6,524,521. Apart from process described above, other known techniques may also be employed to form the fibers. In one aspect, for example, the fibers may be quenched after they are formed and then directly deposited onto a forming wire without first being drawn in the manner described above. In such aspects, as described above, the flow rate of this air flow can be kept relatively low to enhance the tendency of the fibers to remain oriented in the MD direction, however, it should be understood that, in one aspect, the fibers are not oriented in primarily the MD direction.

Referring again to FIG. 1 , once the fibers 23 are formed, they may be heated by a diffuser 33, which can blow hot air onto the surface of the fibers to lightly bond them together for further processing. A hot air knife may also be employed as an alternative to the diffuser. Other techniques for providing integrity to the web may also be employed, such heated calender rolls. In any event, the resulting fibers may then be bonded to form a consolidated, coherent nonwoven web structure. Any suitable bonding technique may generally be employed in the present disclosure, such as adhesive or autogenous bonding (e.g., fusion and/or self-adhesion of the fibers without an applied external adhesive). Autogenous bonding, for instance, may be achieved through contact of the fibers while they are semi-molten or tacky, or simply by blending a tackifying resin and/or solvent with polymer composition used to form the fibers. Suitable autogenous bonding techniques may include ultrasonic bonding, thermal bonding, through-air bonding, and so forth. Thermal point bonding, for instance, typically employs a nip formed between two rolls, at least one of which is patterned. Ultrasonic bonding, on the other hand, typically employs a nip formed between a sonic horn and a patterned roll.

The particular nature of the bonding pattern can vary as desired. One suitable bond pattern, for instance, is known as an “S-weave” pattern and is described in U.S. Pat. No. 5,964,742 to McCormack, et al. Another suitable bonding pattern is known as the “rib-knit” pattern and is described in U.S. Pat. No. 5,620,779 to Levy, et al. Yet another suitable pattern is the “wire weave” pattern, which bond density of from about 200 to about 500 bond sites per square inch, and in some aspects, from about 250 to about 350 bond sites per square inch. Of course, other bond patterns may also be used, such as described in U.S. Pat. No. 3,855,046 to Hansen et al.; U.S. Pat. No. 5,962,112 to Haynes et al.; U.S. Pat. No. 6,093,665 to Sayovitz et al.; D375,844 to Edwards, et al.; D428,267 to Romano et al.; and D390,708 to Brown. Furthermore, a bond pattern may also be employed that contains bond regions that are generally oriented in the machine direction and have an aspect ratio of from about 2 to about 100, in some aspects from about 4 to about 50, and in some aspects, from about 5 to about 20. The pattern of the bond regions is also generally selected so that the spunbond web has a total bond area of less than about 50% (as determined by conventional optical microscopic methods), and in some aspects, less than about 30%, such as less than about 25%, such as less than about 20%, such as less than about 17.5%, in one aspect.

Regardless of the type of nonwoven web material formed, the basis weight of the nonwoven web material may generally vary, such as from about 8 grams per square meter (“gsm”) to about 150 gsm, in some aspects from about 15 gsm to about 125 gsm, and in some aspects, from about 25 gsm to about 100 gsm. When multiple nonwoven web materials are used, such materials may have the same or different basis weights.

The spunbond web may also be subjected to one or more additional post-treatment steps as is known in the art. For example, the spunbond web may be stretched in the cross-machine direction using known techniques, such as tenter frame stretching, groove roll stretching, etc. The spunbond web may also be subjected to other known processing steps, such as aperturing, heat treatments, etc.

In one aspect, the spunbond web formed utilizing an elastomeric bicomponent fiber according to the present disclosure may form all or a part of a nonwoven facing of a composite. Of course, it should also be understood that the nonwoven facing may contain additional layers (e.g., nonwoven webs, films, strands, etc.) if so desired. For example, the facing may contain two (2) or more layers, and in some aspects, from three (3) to ten (10) layers (e.g., 3 or 5 layers). In one aspect, for instance, the nonwoven facing may contain an inner nonwoven layer (e.g., meltblown or spunbond) positioned between two outer nonwoven layers (e.g., spunbond). For example, the inner nonwoven layer may be formed from the spunbond web of the present disclosure and one or both of the outer nonwoven layers may be formed from the spunbond web of the present disclosure or a conventional nonwoven web.

Alternatively, the inner nonwoven layer may be formed from the spunbond web of the present disclosure or a conventional nonwoven web and one or both of the outer nonwoven layers may be formed from the spunbond web of the present disclosure. Various techniques for forming laminates of this nature are described in U.S. Pat. No. 4,041,203 to Brock et al.; U.S. Pat. No. 5,213,881 to Timmons. et al.; 5,464,688 to Timmons, et al.; U.S. Pat. No. 4,374,888 to Bornslaeqer; U.S. Pat. No. 5,169,706 to Collier, et al.; and 4,766,029 to Brock et al. The facing may have other configurations and possess any desired number of layers, such as a spunbond-meltblown-meltblown-spunbond (“SMMS”) laminate, spunbond-meltblown (“SM”) laminate, etc.

Regardless of the method in which the spunbond nonwoven web is formed, or the number of layers in the facing, in one aspect, the nonwoven facing may be used in a laminate by laminating the nonwoven facing to an elastic film or other backing, or any other layer as discussed above. Lamination may be accomplished using a variety of techniques, such as by adhesive bonding, thermal point bonding, ultrasonic bonding, etc. The particular bond pattern is not critical to the present disclosure, and any bond pattern, aperture forming, and stretching discussed above in regards to the spunbond web may also be employed for lamination. Nonetheless, in one aspect the laminate described above can have improved bi-axial stretch and/or bending length characteristics by virtue of the elastomeric film and the extensible (or elastomeric) nonwoven web material formed from a bicomponent fiber according to the present disclosure, and the lamination process.

For instance, in one aspect, a stretch ratio of about 1.5 or more, or 2 to 6 or 2.5 to 7.0, or 3.0 to 5.5, is used to achieve the desired degree of tension in the film during lamination. The stretch ratio may be determined by dividing the final length of the film by its original length. The stretch ratio may also be approximately the same as the draw ratio, which may be determined by dividing the linear speed of the film during lamination (e.g., speed of the nip rolls) by the linear speed at which the film is formed (e.g., speed of casting rolls or blown nip rolls).

Whether laminated to a backing or used alone as a nonwoven web, the spunbond web may be used in a wide variety of applications. For example, as indicated above, the spunbond web may be used in an absorbent article. An “absorbent article” generally refers to any article capable of absorbing water or other fluids. Examples of some absorbent articles include, but are not limited to, personal care absorbent articles, such as diapers, training pants, absorbent underpants, incontinence articles, feminine hygiene products (e.g., sanitary napkins, pantiliners, etc.), swim wear, baby wipes, and so forth; medical absorbent articles, such as garments, fenestration materials, underpads, bedpads, bandages, absorbent drapes, and medical wipes; food service wipers; clothing articles; and so forth, and may be uniquely situated for wearable articles due to its improved garment-like feel.

Several examples of such absorbent articles are described in U.S. Pat. No. 5,649,916 to DiPalma, et al.; U.S. Pat. No. 6,110,158 to Kielpikowski; U.S. Pat. No. 6,663,611 to Blaney, et al. Still other suitable articles are described in U.S. Patent Application Publication No. 2004/0060112 A1 to Fell et al., as well as U.S. Pat. No. 4,886,512 to Damico et al.; U.S. Pat. No. 5,558,659 to Sherrod et al.; U.S. Pat. No. 6,888,044 to Fell et al.; and 6,511,465 to Freiburger et al. Materials and processes suitable for forming such absorbent articles are well known to those skilled in the art. Typically, absorbent articles include a substantially liquid-impermeable layer (e.g., outer cover), a liquid-permeable layer (e.g., bodyside liner, surge layer, etc.), and an absorbent core. In one particular aspect, the composite of the present disclosure may be used in providing a waist section, leg cuff/gasketing, ears, side panels, or an outer cover.

The present invention may be better understood with reference to the following examples.

Test Methods

Burst Strength

Burst strength is a measure of the ability of a fibrous structure to absorb energy, when subjected to deformation normal to the plane of the fibrous structure. Burst strength may be measured in general accordance with ASTM D-6548 with the exception that the testing is done on a Constant-Rate-of-Extension (MTS Systems Corporation, Eden Prairie, Minn.) tensile tester with a computer-based data acquisition and frame control system, where the load cell is positioned above the specimen clamp such that the penetration member is lowered into the test specimen causing it to rupture. The arrangement of the load cell and the specimen is opposite that illustrated in FIG. 1 of ASTM D-6548. The penetration assembly consists of a semi spherical anodized aluminum penetration member having a diameter of 1.588±0.005 cm affixed to an adjustable rod having a ball end socket. The test specimen is secured in a specimen clamp consisting of upper and lower concentric rings of aluminum between which the sample is held firmly by mechanical clamping during testing. The specimen clamping rings has an internal diameter of 8.89±0.03 cm.

The tensile tester is set up such that the crosshead speed is 15.2 cm/min, the probe separation is 104 mm, the break sensitivity is 60 percent and the slack compensation is 10 gf and the instrument is calibrated according to the manufacturer's instructions.

Samples are conditioned under TAPPI conditions and cut into 127×127 mm±5 mm squares. For each test a total of 3 sheets of product are combined. The sheets are stacked on top of one another in a manner such that the machine direction of the sheets is aligned. Where samples comprise multiple plies, the plies are not separated for testing. In each instance the test sample comprises 3 sheets of product. For example, if the product is a 2-ply tissue product, 3 sheets of product, totaling 6 plies are tested. If the product is a single ply tissue product, then 3 sheets of product totaling 3 plies are tested.

Prior to testing the height of the probe is adjusted as necessary by inserting the burst fixture into the bottom of the tensile tester and lowering the probe until it was positioned approximately 12.7 mm above the alignment plate. The length of the probe is then adjusted until it rests in the recessed area of the alignment plate when lowered.

It is recommended to use a load cell in which the majority of the peak load results fall between 10 and 90 percent of the capacity of the load cell. To determine the most appropriate load cell for testing, samples are initially tested to determine peak load. If peak load is <450 gf a 10 Newton load cell is used, if peak load is >450 gf a 50 Newton load cell is used.

Once the apparatus is set-up and a load cell selected, samples are tested by inserting the sample into the specimen clamp and clamping the test sample in place. The test sequence is then activated, causing the penetration assembly to be lowered at the rate and distance specified above. Upon rupture of the test specimen by the penetration assembly the measured resistance to penetration force is displayed and recorded. The specimen clamp is then released to remove the sample and ready the apparatus for the next test.

The peak load (gf) and energy to peak (g-cm) are recorded.

Softness/Cup Crush Test:

The softness of a nonwoven fabric may be measured according to the “cup crush” test. The cup crush test evaluates fabric stiffness by measuring the peak load (also called the “cup crush load” or just “cup crush”) and the energy required to crush a specimen and in turn quantify softness of the specimen. The specimen is placed inside a forming cup. The forming cup and the specimen are then placed on a load plate which is mounted on a tensile tester. A foot descends through the open end of the forming cup and “crushes” and distorts the cup-shaped specimen inside. Peak load measured in gramsforce (go and Energy, measured in gramsforce-length (gf-mm) are the results. The results are a manifestation of the stiffness of the material. The stiffer the material, the higher the peak load and energy values. The softer the material, the lower the values.

The constant rate of extension tensile tester is equipped with a computerized data-acquisition system (such as MTS TestWorks for Windows version 4, from MTS Systems Corporation, Eden Prairie, Minn. 55344-2290) that is capable of calculating peak load and energy, preferably at a minimum data capture rate of 20 data points per second, between two pre-determined distances (15-60 millimeters) in a compression mode. A suitable device for measuring cup crush is a model FTD-G-500 load cell (500 gram range) available from the Schaevitz Company, Pennsauken, N.J. Tensile Testers and load cells can be obtained from Instron Corporation, Canton, Mass. 02021 or Sintech, Inc., P.O. Box 14226, Research Triangle Park, N.C. 27709-4226.

The energy measured is that required for a 4.5 cm diameter hemispherically shaped foot to crush a 23 cm by 23 cm piece of fabric shaped into an approximately 6.5 cm diameter by 6.5 cm tall inverted cup while the cup shaped fabric is surrounded by an approximately 6.5 cm diameter cylinder (forming cup) to maintain a uniform deformation of the cup shaped fabric during testing. An average of 3-5 readings was used. The test is conducted in a standard laboratory atmosphere of 23±2° C. and 50±5% relative humidity. The material should be allowed to reach ambient temperature before testing. The specimen is prepared by placing a retaining ring over a forming stand. The material is then placed over the forming stand. A forming cup is placed over the specimen and the forming stand to conform the specimen into the cup shape. The retaining ring engages the forming cup to secure the specimen in the forming cup. The forming cup is removed with the now-formed specimen inside. The specimen is secured within the forming cup by the retaining ring. The specimen, forming cup, and retaining ring are inverted and placed in the tensile tester. The foot and the forming cup are aligned in the tensile tester to avoid contact between the cup walls and the foot which could affect the readings. The foot (0.5 inch and either made of lightweight nylon or metal) passes through an opening in the bottom of the inverted forming cup to crush the cup-shaped sample inside. The peak load is measured while the foot is descending at a rate of about 406 mm per minute and is measured in grams. The cup crush test also yields a value for the total energy required to crush a sample (the “cup crush energy”) which is the energy from the start of the test to the peak load point, i.e. the area under the curve formed by the load in grams on one axis and the distance the foot travels in millimeters on the other. Cup crush energy is therefore reported in gf-mm. Lower cup crush values indicate a softer laminate.

Multi-Cycle Stress/Strain Test for Raw Materials

The Multi-cycle Stress/Strain Test is a two-cycle elongation and recovery test used to measure the elongation and recovery characteristics of elastic raw materials and elastic material composites. In particular, the test may be used to determine what effects, if any, the application of the described formulations to the substrates have on the elongation and recovery characteristics thereof. Deterioration of substrate properties measured by this test are those that manifest as a loss of tension, or resistance to elongation, which may result in extreme elongation on application of a force, as with sagging.

The test measures load values of a test sample placed under a particular amount of strain (e.g., elongated to a particular elongation). Such load values are determined during both the elongation and recovery phases of the test, and during each of the two cycles. For this example, the load values was set at 30% elongation. In general, a decrease in the amount of the load retained after treatment indicates a negative impact on the elastic characteristics of the substrate, even in the absence of visible deterioration or delamination of the substrate.

Hysteresis is a measure of how well an elastic material retains its elastic properties over a number of stretches. It is the mechanical energy loss occurring during the loading and unloading cycles, and it is illustrated by the area between the loading and unloading curves. The lower the Hysteresis Loss, the more the NBL/EMC retains its elastic behavior and the more it acts like a rubber band. This is critical in diaper fit performance to ensure the ears do their fastening job even after multiple stretches.

Percent Set is the permanent deformation caused by loading. Because the NBL/EMC material loses some energy when being pulled, it does not return to exactly 0 grams when the retraction cycle returns to 0% elongation. The lower the Percent Set, the better elastic characteristic and the more like a rubber band the material behaves which helps with fit performance.

Strip Tensile Peak Load

After the elongation is completed, the sample was held between grips having a front and back face measuring 25.4 millimeters×76 millimeters. The grip faces were rubberized, and the longer dimension of the grip was perpendicular to the direction of pull. The grip pressure was pneumatically maintained at a pressure of 40 pounds per square inch. The tensile test was run at a 300-millimeter per minute rate with a gauge length of 76 millimeters and a break sensitivity of 40%.

Three samples were tested by applying the test load along the machine-direction and three samples were tested by applying the test load along the cross direction. In addition to tensile strength, the peak load, peak stretch (i.e., % elongation at peak load), and the energy to peak was measured. The peak strip tensile loads from each specimen tested were arithmetically averaged to determine the MD or CD tensile strength.

Effusivity

The thermal effusivity of the sample was measured with a C-Therm TCi Thermal Conductivity Analyzer in accordance with ASTM D7984-16 Standard (“Test Method for Measurement of Thermal Effusivity of Fabrics Using a Modified Transient Plane Source (MTPS) Instrument.”) The default C-Therm TCi Thermal Conductivity Analyzer employs the Modified Transient Plane Source (MTPS) technique in characterizing the thermal conductivity and effusivity of materials. It employs a one-sided, interfacial heat reflectance sensor that applies a momentary constant heat source to the sample.

Example 1

Spunbond nonwoven webs were formed using bicomponent fibers having core compositions shown in Table 2. The sheath was 98% Dow ASPUN© 6840A Ethylene Polymer with 2 wt. % pigment. After formation, the spunbond webs were subjected to various tests for strength, elasticity, softness and spinnability, the results of which are shown in Table 2.

TABLE 2 Burst Spunbond Spunbond Basis Peak Cup Crush Vistamaxx Versify Versify Secondary Polypropylene Polypropylene Weight Load Peak Load Effusivity 7050 4301 4200 Amide¹ 3166 3155 (Gsm) (gf (gf) (Ws^(1/2)/m²K) Comparative 1 95 5 51.5 947.9 8.5 145.4 Comparative 2 93 5 2 48.8 986.9 7.9 — Sample 1 70 25 5 48.4 1101.3 9.4 — Sample 2 45 50 5 50.1 1470.5 7.3 151.2 Sample 3 43 50 5 2 49.5 1618.3 8.2 143.1 Sample 4 43 50 5 2 51.0 1311.4 11.0 145.4 Control 100 47.0 2826.5 103.1  88.6 ¹Concentrate containing 15 wt. % of a secondary amide as described above, for an active amount of 0.75 wt. % secondary amide in the core

Example 2

Fibers were formed in the same manner as Example 1, except core blends were used according to Table 3. A FTIR spectra was obtained from the fibers formed in Example 2 according to the FTIR Peak Ratio defined above. As shown in FIGS. 3A and 3B, the peak at 842 cm⁻¹ was measured, which represents CH₂ rocking and C—CH₃ stretching and is an indication of a more ordered packing of a propylene polymer chain. Additionally, a peak at 974 cm⁻¹ was measured, which represents CH₃ rocking and C—C stretching and is associated with more amorphous polypropylene. Thus, according to Example 2, a ratio of about 0.5 or more of the 842 cm⁻¹ peak to the 974 cm⁻¹ indicates a more ordered structure than can be obtained using Vistamax or Versify alone, which is further illustrated in FIG. 3C.

TABLE 3 Spunbond Vistamaxx Versify Secondary Polypropylene 7050 4301 Amide¹ 3854 Code 1 35 50 5 10 Code 2 95 5 Code 3 60 25 5 10 Code 4  0 85 5 10

While the disclosure has been described in detail with respect to the specific aspects thereof, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing, may readily conceive of alterations to, variations of, and equivalents to these aspects. Accordingly, the scope of the present disclosure should be assessed as that of the appended claims and any equivalents thereto. 

What is claimed:
 1. A nonwoven web comprising an elastomeric bicomponent fiber, the elastomeric bicomponent fiber comprising: a core comprising at least two polypropylene based elastomers and a secondary amide; and at least one sheath; wherein the at least one sheath comprises less than 50 wt. % of the total weight of the bicomponent fiber; and wherein the nonwoven web exhibits a peak burst load of about 1100 gf or greater based upon a nonwoven web having a basis weight of about 48 grams per square meter (gsm) or a normalized peak burst load of about 22 gf/gsm.
 2. The nonwoven web of claim 1, wherein the nonwoven web exhibits a cup crush bending stiffness of about 100 gf or less based upon a nonwoven web having a basis weight of about 48 grams per square meter (gsm) or a normalized cup crush bending stiffness of about 2.1 gf/gsm or less.
 3. The nonwoven web of claim 1, wherein the nonwoven web exhibits an effusivity of about 90 Ws^(1/2)/m²K or greater.
 4. The nonwoven web of claim 1, wherein the at least two polypropylene based elastomers comprise an ethylene copolymer, α-olefin copolymer, or a combination thereof.
 5. The nonwoven web of claim 1, wherein the sheath comprises a non-elastomeric polymer.
 6. The nonwoven web of claim 1, wherein the sheath comprises a polyethylene polymer.
 7. The nonwoven web of claim 1, wherein the secondary amide is present in the core in an amount of about 0.1% to about 10% by weight based upon the weight of the core.
 8. The nonwoven web of claim 1, wherein the secondary amide is present in the core in an amount of about 0.25% to about 5% by weight based upon the weight of the core.
 9. The nonwoven web of claim 1, wherein the secondary amide is a fatty acid amide.
 10. The nonwoven web of claim 1, wherein the at least two polypropylene based elastomer comprise a propylene/ethylene copolymer.
 11. The nonwoven web of claim 1, wherein at least one of the sheath and the core further comprises pigment particles.
 12. The nonwoven web of claim 1, wherein the pigment particles are present in the at least one of the sheath and the core in an amount of about 0.1% to about 5% by weight based upon the weight of the sheath or the core.
 13. The nonwoven web of claim 1, wherein the core further comprises about 5 wt. % or less of a polypropylene homopolymer, based upon the weight of the core.
 14. An elastomeric laminate comprising a spunbond nonwoven web according to claim 1, and a backing.
 15. The elastomeric laminate of claim 14, wherein the backing comprises an elastic film.
 16. An absorbent article formed from the nonwoven web of claim
 1. 17. An elastomeric bicomponent fiber comprising: a core comprising at least two polypropylene based elastomers and a secondary amide; and at least one sheath; wherein the at least one sheath comprises less than 50 wt. % of the total weight of the bicomponent fiber; and wherein the elastomeric bicomponent fiber exhibits a FTIR peak height ratio of an 842 cm⁻¹ peak to an 974 cm⁻¹ peak of about 0.525 or greater, as measured using a Perkin Elmer Frontier FTIR spectrometer, based upon an average of 32 scans at 4 cm⁻¹ resolution.
 18. The elastomeric bicomponent fiber of claim 17, wherein the at least two polypropylene based elastomers include a first polypropylene based elastomer and a second polypropylene based elastomer, wherein the first polypropylene based elastomer comprises about 30 wt. % or more of the core, based upon the weight of the core.
 19. The elastomeric bicomponent fiber of claim 18, wherein the second polypropylene based elastomer comprises about 60 wt. % or less of the core, based upon the weight of the core.
 20. The elastomeric bicomponent fiber of claim 17, wherein the core further comprises about 15 wt. % or less of a polypropylene homopolymer. 